[Epidemic situation of HIV/AIDS and change trend in Belt and Road countries].

Objective: To understand the epidemic situation of HIV/AIDS and its change trend in the Belt and Road countries and provide evidence for the improvement of prevention and control of the cross-border transmission of HIV/AIDS. Methods: The 145 countries that have signed the cooperation document of the Belt and Road initiative with China were selected in our study. Age-standardized incidence rate and prevalence rate of HIV/AIDS in the 145 countries from 2013 to 2019 were downloaded from the Global Burden of Disease Study 2019. Age-standardized incidence rate and prevalence rate of HIV/AIDS in 2019 were used to describe the HIV/AIDS epidemics in 145 countries, and the estimated annual percentage change (EAPC) of incidence was calculated to analyze the trend of HIV/AIDS incidence from 2013 to 2019. Results: In 2019, Africa had the highest proportion of countries with HIV/AIDS incidence exceeding 40.00 per 100 000 (56.86%, 29/51), and Asia had the lowest proportion (5.41%, 2/37). The countries with the prevalence rate of HIV/AIDS exceeding 100.00 per 10 000 were almost distributed in Africa, accounting for 20.69% (30/145). From 2013 to 2019, the incidence rate of HIV/AIDS increased in 50 countries, accounting for 34.48% (50/145). The incidence rate of HIV/AIDS showed downward trends in 69 countries (47.59%, 69/145), and showed no significant change in 26 countries (17.93%, 26/145). The most obvious increase of incidence rate of HIV/AIDS was observed in Comoros (EAPC=15.60, 95%CI: 5.84-26.26) and the most obvious decrease was observed in Burundi (EAPC=-14.27, 95%CI: -15.21 to -13.31). Conclusions: In the Belt and Road countries, the most severe disease burden of HIV/AIDS was observed in countries in Africa, and the incidences of HIV/AIDS increased rapidly in some European countries, which means the risk of cross-border transmission still exists. Hence, the prevention and control of HIV/AIDS in China should be further strengthened in the future.

[Epidemic situation of multidrug-resistant tuberculosis and change trend in Belt and Road countries].

Objective: To analyze the epidemic situation of multidrug-resistant tuberculosis in 2019 and the incidence trends from 2013 to 2019 in the Belt and Road countries. Methods: The 145 countries that have signed cooperation documents of the Belt and Road Initiative with China were selected. Age-standardized incidence and prevalence rate of multidrug-resistant tuberculosis from the Global Burden of Disease Study were used to describe the epidemic situation of multidrug-resistant tuberculosis in 2019. The annual percentage changes of the age-standardized incidence rate were calculated to assess incidence trends of multidrug-resistant tuberculosis from 2013 to 2019. Results: In 2019, of the 145 countries, Somalia had the highest incidence rate (30.42 per 100 000) and prevalence rate (48.86 per 100 000) of multidrug-resistant tuberculosis, while Slovenia had the lowest incidence rate (0.01 per 100 000) and prevalence rate (0.01 per 100 000). The incidence trends of multidrug-resistant tuberculosis in six continents from 2013 to 2019 were as follows: multidrug-resistant tuberculosis incidence rates showed increasing trends in 14 countries (27.45%) and decreasing trends in 22 countries (43.14%) in Africa, showed increasing trends in 2 countries (18.18%) and decreasing trends in 3 countries (27.27%) in North America and showed increasing trends in 2 countries (5.41%) and decreasing trends in 23 countries (62.16%) in Asia. The increasing trends were observed in Europe, Oceania, and South America, but it was found that 26 countries (96.30%) in Europe, 2 countries (18.18%) in Oceania, and 1 country (12.50%) in South America had decreasing trends of multidrug-resistant tuberculosis incidence rates. Conclusion: Multidrug-resistant tuberculosis is endemic in 145 Belt and Road countries with the prevalence increasing year by year in some countries in central and southern Africa and decreasing in European countries except Ukraine.

[Epidemic situation and trend of dengue fever in Belt and Road countries].

Objective: To analyze epidemic situation of dengue fever in 2019 and the incidence trends from 2013 to 2019 in the Belt and Road countries. Methods: We used age-standardized incidence rate (ASR) which was from Global Burden of Disease Study 2019 to describe the epidemic situation of dengue fever in 2019. The estimated annual percentage change(EAPC) of the ASR was calculated to assess dengue fever incidence trends from 2013 to 2019. Results: The 2019 GBD dengue fever incidence records showed that in 145 Belt and Road countries, 93 (64.14%) countries had dengue fever epidemics. In 2019, there were 11 countries with the incidence >3 000.00 per 100 000, including 9 countries in Oceania; 16 countries with the incidence of 1 000.00 per 100 000-2 999.99 per 100 000, including 10 countries in Asia. The incidence rates in most countries in Africa (58.14%,25/43), North America (72.73%,8/11) and South America (66.67%,4/6) ranged from 500.00 per 100 000 to 999.99 per 100 000. The incidence rates of dengue fever in 90.00% (9/10) of countries in Oceania showed increasing trend, and the increasing trend in Fiji was most obvious (EAPC=18.22,95%CI:12.91-23.77), and the incidence rates of dengue fever in 18.18% (4/22) of countries in Asia showed increasing trend, the increasing trend in the Philippines was most obvious (EAPC=3.09,95%CI:1.74-4.45), and the incidence rates of dengue fever in 4.65% (2/43) of countries in Africa showed increasing trend, and the increasing trend in Seychelles was most obvious (EAPC=18.20,95%CI:7.82-29.58). The incidence rates of dengue fever showed no increasing trend in countries in South America and North America. Conclusions: In 2019, more than 60% of the Belt and Road countries had dengue fever epidemics. The incidences of dengue fever were high and showed increasing trends in most Oceanian countries, but the dengue fever epidemics in the countries in Asia, Africa and Americas were relatively mild.

[Epidemic situation of malaria and change trend in Belt and Road countries].

Objective: To understand the epidemic situation of malaria and its change trend in the Belt and Road countries. Methods: The 145 countries with which China has signed cooperation documents on the Belt and Road Initiative were selected for this study, and their malaria incidence data were collected from the Global Burden of Disease 2019. The age-standardized incidence rate (ASR) was used to describe the epidemic situation of malaria in 2019. The estimated annual percentage change (EAPC) of the ASR was calculated to assess the incidence trend of malaria from 2013 to 2019. Results: Among the 145 countries, 74 (51.03%) countries had malaria epidemics, mainly in Africa (60.81%, 45/74) and Asia (22.97%, 17/74). The countries with malaria incidence of ≥10 000 per 100 000 in 2019 were mainly distributed in Africa (96.15%, 25/26). From 2013 to 2019, the incidence rates of malaria showed decreasing trends in 32 countries (43.24%), and the incidence rates of malaria in 23 countries (31.08%) showed no significant change, while the incidence rates of malaria in 19 countries (25.68%) showed increasing trends. The obvious increasing trends were observed in Cape Verde (EAPC=151.46, 95%CI: 47.15-329.71), South Africa (EAPC=98.61, 95%CI: 32.11-198.58) and Namibia (EAPC=78.03, 95%CI: 54.30-105.42). Conclusion: About half of the Belt and Road countries had malaria epidemics in 2019, in which 1/4 had increased incidence of malaria. China should continue to strengthen the prevention and control of malaria, especially imported malaria, to maintain the achievements of malaria elimination.

Sevoflurane impedes the progression of glioma through modulating the circular RNA has_circ_0012129/miR-761/TGIF2 axis.

OBJECTIVE: Glioma is a highly aggressive and lethal brain tumor. Anesthetics have been shown to have important effects on the biological characteristics of cancer cells. Nevertheless, the molecular mechanism of anesthetic-mediated glioma cells progression remains unclear. MATERIALS AND METHODS: Sevoflurane (sev) was employed to treat glioma cells. The biological characteristics (viability, colony formation, apoptosis, cell cycle, migration, and invasion) of glioma cells were determined via Cell Counting Kit-8 (CCK-8), cell colony formation, flow cytometry, PI cytometry, or transwell assays. The protein levels of Cell Cycle Dependent Kinase (CDK) 2, CDK4, E-cadherin, N-cadherin, Vimentin, and Transforming Growth Factor Beta (TGFB) induced factor homeobox 2 (TGIF2) were assessed through Western blot analysis. Glucose consumption and lactate production were measured using special commercial kits. The expression of circular RNA has_circ_0012129 (circ_0012129) and miR-761 was detected via quantitative Real Time-Polymerase Chain Reaction (qRT-PCR). The relationship between circ_0012129 or TGIF2 and miR-761 was verified with Dual-Luciferase reporter assay. Sevoflurane-mediated molecular mechanisms have been confirmed via xenograft assay. RESULTS: Sevoflurane suppressed viability, colony formation, cell cycle, migration, and invasion and promoted apoptosis of glioma cells in vitro, and impeded tumor growth in vivo. Circ_0012129 and TGIF2 were downregulated and miR-761 was upregulated in sevoflurane-treated glioma cells. Circ_0012129 elevation abolished sevoflurane-mediated biological characteristics of glioma cells. MiR-761 served as target for circ_0012129 and miR-761 targeted TGIF2. Moreover, both miR-761 overexpression and TGIF2 suppression restored circ_0012129 enhancement-mediated biological characteristics of sevoflurane-treated glioma cells. CONCLUSIONS: Sevoflurane mediated the progression of glioma via regulating the circ_0012129/miR-761/TGIF2 axis.

Cost effectiveness and delivery study for future HIV vaccines.

Research teams from five countries, Brazil, China, Kenya, Peru and Thailand, have initiated a policy-maker survey on vaccine delivery, cost studies for future HIV vaccination programmes, and associated simulation modeling exercises analysing the relative cost-effectiveness of potential HIV vaccination strategies. The survey assesses challenges and opportunities for future country-level HIV vaccination strategies, providing data on the vaccine characteristics (e.g. vaccine efficacies for susceptibility, infectiousness and disease progression) and vaccination programme strategies to be considered in the cost-effectiveness modeling analyses. The study will provide decision-makers with modeling data on vaccination policy considerations that will assist in developing country-level capacities for future HIV vaccine policy adoption and effective delivery systems, and will help delineate the long-term financial requirements for sustainable HIV vaccination programmes. The WHO-UNAIDS HIV Vaccine Initiative and the collaborating researchers welcome comments or questions from policy makers, health professionals and other stakeholders in the public and private sectors about this effort to help advance policy and capacity related to future potential HIV vaccines.

Prevalence of TT virus and GBV-C infections among patients with liver diseases and the general population in Shanghai, China.

To determine the prevalence of TT virus (TTV) and GB virus C/hepatitis G virus (GBV-C) infections among patients with liver disease and the general population in Shanghai, China, we studied 90 patients with liver diseases (acute hepatitis, 28; chronic hepatitis, 27; liver cirrhosis, 20; hepatocellular carcinoma, 15) and 90 age, sex matched healthy blood donors as controls. There were no significant differences in the clinical and demographic characteristics between the two groups, except for liver function test values. There was a statistical difference between the patient group and the control group with regard to the prevalence of TTV DNA (23.5% in patient group, 11.1% in control group, P < 0.05), although no differences in clinical features could be found between TTV DNA-positive and negative subjects. Also, no differences in TTV DNA prevalence among various categories of liver diseases were noted (P = NS). The prevalence of HBsAg was significantly different between the patient group (36.7%) and the control group (3.3%) (P0.01), whereas the prevalence of anti-HCV and GBV-C RNA were not significantly different between the two groups. The nucleotide sequences were determined in the TTV DNA-positive samples and evaluated using phylogenetic analysis which suggested that they could be divided into two main genotypes designated as genotype 1 and 2. There were five samples clustered into 3 hitherto unknown subtypes of genotype 2. We concluded that (1) although TTV infection is widespread among both groups and there is a statistical difference of TTV infection between them, no hepatic damaging evidence and correlation with certain liver disease could be found in this study, suggest that TTV may not be major cause of liver disease, (2) GBV-C infection is frequent, but the virus is not the cause of liver diseases, and (3) new subtypes of TTV may exist in Shanghai, China.

Chinese herbal formula XQ-9302: pilot study of its clinical and in vitro activity against human immunodeficiency virus.

OBJECTIVES: To evaluate the effectiveness of XQ-9302--a purified, precise mixture of 20 Chinese herbs--against infection with human immunodeficiency virus in vitro and in the clinic. DESIGN: In vitro cell culture assay, heavy metal content analysis, and pilot non-randomised clinical trial. SETTING: Drug rehabilitation centre and municipal surveillance centre, Shanghai, China. PATIENTS: Forty-eight patients who had various clinical histories, such as drug abuse, cancer, and infection with human immunodeficiency virus, participated in the clinical study. INTERVENTION: During the clinical trial, multiple 15-day courses of XQ-9302 10.8 g/d were given to participants. MAIN OUTCOME MEASURES: CD4 count, P24 antigen level, level of antibody against human immunodeficiency virus, number of copies per millilitre of human immunodeficiency virus in the plasma (viral load), and any side effects. RESULTS: XQ-9302 protected cultured MT4 cells from infection with human immunodeficiency virus in vitro. Clinical tests showed that the herbal formula relieved the symptoms of acquired immunodeficiency syndrome and enhanced CD4 counts in patients infected by the human immunodeficiency virus. There were no observable side effects, even after taking the drug for several months. In three patients who had acquired immunodeficiency syndrome, treatment with XQ-9302 reduced the magnitude of the viral load by more than 1 log. CONCLUSION: XQ-9302 not only improves the immune function of patients infected with the human immunodeficiency virus, but also interrupts viral replication and slows the progression of the disease without detectable side effects. In addition, the heavy metal content of XQ-9302 is well within safety levels set by the Government of China.

Differential expression in human cells from the p6 promoter of human parvovirus B19 following plasmid transfection and recombinant adeno-associated virus 2 (AAV) infection: human megakaryocytic leukaemia cells are non-permissive for AAV infection.

Expression from the human parvovirus B19p6 promoter fused to the firefly luciferase ('Luc') reporter gene was evaluated in a non-erythroid human nasopharyngeal carcinoma cell line, KB, and a human megakaryocytic leukaemia cell line, MB-02, known to become permissive for B19 replication following erythroid-differentiation. The B19p6-Luc construct was introduced into KB and MB-02 cells, both in undifferentiated and differentiated states, either via DNA-mediated transfection, or via infection with recombinant adeno-associated virus 2 (AAV), a non-pathogenic human parvovirus known to possess a broad host-range. Although Luc activity was readily detected in KB cells following transfection of the B19p6-Luc plasmid DNA, no expression from the B19p6 promoter was observed following infection with recombinant virus. In addition, transfection of the reporter plasmid resulted in high-level expression of Luc in differentiated but not in undifferentiated MB-02 cells. However, no Luc activity was detected, even in differentiated MB-02 cells, following infection with recombinant virus. Further studies with an additional recombinant as well as wild-type (wt) AAV revealed that MB-02 cells were non-permissive for AAV infection. A second human megakaryocytic leukaemia cell line, M07e, was likewise resistant to infection by recombinant as well as wt AAV. Taken together, these studies identify the first human cell type that cannot be infected by AAV. They indicate that expression from the B19p6 promoter, in the context of an AAV genome, is restricted to primary human haematopoietic cells, perhaps because parvoviral DNA replication and transcription are intrinsically coupled.

Multiple transcription factors are required for activation of human interleukin 9 gene in T cells.

The genetic elements and regulatory mechanisms responsible for human interleukin 9 (IL-9) gene expression in a human T cell leukemia virus type I-transformed human T cell line, C5MJ2, were investigated. We demonstrated that IL-9 gene expression is controlled, at least in part, by transcriptional activation. Transient expression of the luciferase reporter gene linked to serially deleted sequences of the 5'-flanking region of the IL-9 gene has revealed several positive and negative regulatory elements involved in the basal and inducible expression of the IL-9 gene in C5MJ2 cells. An AP-1 site at -146 to -140 was shown to be involved in the expression of the IL-9 gene. A proximal region between -46 and -80 was identified as the minimum sequence for the basal and inducible expression of the IL-9 gene in C5MJ2 cells. Within this region, an NF-kappaB site at -59 to -50 and its adjacent 20-base pair upstream sequence were demonstrated to play a critical role for the IL-9 promoter activity. DNA-protein binding studies indicated that NF-kappaB, c-Jun, and potentially novel proteins (around 35 kDa) can bind to this important sequence. Mutations at different sites within this proximal promoter region abolished the promoter activity as well as the DNA binding. Taken together, these results suggest that the cooperation of different transcription factors is essential for IL-9 gene expression in T cells.

Activation of junB and c-myc primary response genes by interleukin 9 in a human factor-dependent cell line.

Interleukin 9 (IL-9) stimulates the proliferation of various hematopoietic cell types. To elucidate the molecular mechanisms underlying the cell proliferation action, immediate-early gene expression elicited by IL-9 in a human factor-dependent cell line, MO7e, was studied. IL-9 stimulation resulted in a rapid and transient elevation of primary response genes including junB and c-myc. The differential effects of protein kinase inhibitors, herbimycin A, genistein, and H-7 on the steady-state mRNA level and the transcription rate of junB and c-myc genes triggered by IL-9 were also investigated. Herbimycin A, but not genistein, specifically inhibited the expression of junB steady-state mRNA and the in vitro transcription of the junB gene. IL-9-enhanced c-myc gene expression was completely inhibited by both herbimycin A and genistein at the level of transcriptional initiation. H-7 failed to inhibit c-myc, but partially abolished junB mRNA induction. The role of protein kinase C in IL-9-mediated junB induction was also examined. The different responses of junB and c-myc messages to protein kinase inhibitors suggested that more than one pathway may be involved in IL-9-mediated signal transduction which leads to the expression of junB and c-myc genes.

Molecular and functional interactions of transcription factor USF with the long terminal repeat of human immunodeficiency virus type 1.

The human transcription factor USF, purified from HeLa cells, and its recombinant 43-kDa component bind to the long terminal repeat (LTR) of human immunodeficiency virus type 1. The proteins footprint over nucleotides from position -173 to -157 upstream of the transcription start site, generating strong DNAse I hypersensitivity sites at the 3' sides on both strands. As detected by methylation protection studies, the factor forms symmetric contacts with the guanines of the palindromic CACGTG core of the recognized sequence. Its binding ability is abolished by the mutation of this core sequence and is strongly reduced by the cytosine methylation of the central CpG dinucleotide. Upon binding, both recombinant and purified USFs bend the LTR DNA template. The role of USF in the control of transcription initiation from the LTR was tested by in vitro transcription assays. Upon addition of the protein, transcription from constructs containing an intact binding site is increased, while the responsiveness in constructs with a mutated sequence is abolished. Furthermore, the addition of a decoy plasmid which contains multiple repeats of the target sequence results in downregulation of transcription from the LTR. These results suggest that USF is a positive regulator of LTR-mediated transcriptional activation.

Adeno-associated virus 2-mediated high efficiency gene transfer into immature and mature subsets of hematopoietic progenitor cells in human umbilical cord blood.

Recombinant adeno-associated virus 2 (AAV) virions were constructed containing a gene for resistance to neomycin (neoR), under the control of either the herpesvirus thymidine kinase (TK) gene promoter (vTK-Neo), or the human parvovirus B19 p6 promoter (vB19-Neo), as well as those containing an upstream erythroid cell-specific enhancer (HS-2) from the locus control region of the human beta-globin gene cluster (vHS2-TK-Neo; vHS2-B19-Neo). These recombinant virions were used to infect either low density or highly enriched populations of CD34+ cells isolated from human umbilical cord blood. In clonogenic assays initiated with cells infected with the different recombinant AAV-Neo virions, equivalent high frequency transduction of the neoR gene into slow-cycling multipotential, erythroid, and granulocyte/macrophage (GM) progenitor cells, including those with high proliferative potential, was obtained without prestimulation with growth factors, indicating that these immature and mature hematopoietic progenitor cells were susceptible to infection by the recombinant AAV virions. Successful transduction did not require and was not enhanced by prestimulation of these cell populations with cytokines. The functional activity of the transduced neo gene was evident by the development of resistance to the drug G418, a neomycin analogue. Individual high and low proliferative colony-forming unit (CFU)-GM, burst-forming unit-erythroid, and CFU-granulocyte erythroid macrophage megakaryocyte colonies from mock-infected, or the recombinant virus-infected cultures were subjected to polymerase chain reaction analysis using a neo-specific synthetic oligonucleotide primer pair. A 276-bp DNA fragment that hybridized with a neo-specific DNA probe on Southern blots was only detected in those colonies cloned from the recombinant virus-infected cells, indicating stable integration of the transduced neo gene. These studies suggest that parvovirus-based vectors may prove to be a useful alternative to the more commonly used retroviral vectors for high efficiency gene transfer into slow or noncycling primitive hematopoietic progenitor cells, without the need for growth factor stimulation, which could potentially lead to differentiation of these cells before transplantation.

An efficacy trial of a mammalian cell-derived recombinant DNA hepatitis B vaccine in infants born to mothers positive for HBsAg, in Shanghai, China.

We conducted a randomized, double-blind clinical trial of an experimental mammalian cell-derived DNA hepatitis B vaccine (Betagen, Connaught Laboratories Ltd, Toronto, Canada) to determine its efficacy in infants born to mothers who were carriers of hepatitis B surface antigen (HBsAg). Four groups of 55 infants received injections as follows: (1) a licensed plasma-derived vaccine (Lanzhou, Lanzhou Institute for Biological Products, Lanzhou, People's Republic of China), 20 micrograms; (2) Betagen, 20 micrograms; (3) Betagen, 20 micrograms+hepatitis B immune globulin (HBIG); and (4) Betagen, 10 micrograms+HBIG. Vaccine injections were given at birth and at 1 and 6 months and HBIG was given at birth. The vaccines were compared to a historical placebo control group. The efficacy of Betagen alone was 82.6% compared to 51.0% for the Lanzhou. Efficacy of Betagen increased with the concomitant use of HBIG. No infants who were HBsAg negative at birth and/or were born to hepatitis B e antigen (HBeAg) negative mothers became carriers. The rate of HBsAg in infants receiving Betagen alone, and born to mothers who were HBeAg positive, decreased from 60% at birth to 20% by the ninth month, compared to 62.5% and 50% (respectively) for Lanzhou. The percentage of infants with protective levels of antiHBs was significantly higher for Betagen alone than for Lanzhou, but the geometric mean titre of antiHBs for responders was not significantly different. We have shown that Betagen alone is highly efficacious in preventing the development of hepatitis B in infants born to mothers who are carriers of HBsAg and is also highly effective in reducing the carriage of HBsAg in infants who are HBsAg positive at birth and/or born to HBeAg positive mothers.

PIP: Researchers assigned 220 infants born at 5 participating hospitals in Shanghai, China to receive either a 20mcg of an experimental recombinant DNA hepatitis B vaccine (Betagen), a licensed plasma derived hepatitis B vaccine (Lanzhou), 20 mcg of Betagen and hepatitis B immune globulin (HBIG), or 10mcg of Betagen and HBIG to determine the efficacy of Betagen in infants born to mothers with hepatitis B surface antigen (HBsAg) positive. Since China is a hyperendemic hepatitis B carrier area (in Shanghai, for example, prevalence rate is 57%), China hopes to reduce the carrier state via a low cost, safe, immunogenic, and efficacious recombinant vaccine. 20mcg of Betagen resulted in 82.6% efficacy which was significantly higher than that of Lanzhou (51%). The efficacy increased when HBIG was administered with the 20mcg of Betagen (92%). None of the infants born HBsAg negative and/or born to hepatitis B e antigen (HBeAg) mothers later became carriers. Further the HBsAg positive fell from 60-2-% in 9 months whereas these corresponding figures for those who received only Lanzhou were 62.5% and 50%. Even though the percentage of infants with protective levels of antiHBs stood much higher in those who received only Betagen than for those who received Lanzhou in all the months of follow up, except the 1st, their geometric mean titre of antiHBs was not statistically significant. Since Betagen prompted a quick antibody response which probably helped decrease HBsAg in the serum of those infants already positive for HBsAg at birth, it had an advantage over Lanzhou. In conclusion, Betagen given alone proved to be very efficacious in preventing hepatitis B in infants born to carriers of HBsAg. Further it was effective in reducing carriage of HBsAg in infants born HBsAg positive and/or born to HBeAg positive mothers.

An epidemic of hepatitis A attributable to the ingestion of raw clams in Shanghai, China.

An epidemic of hepatitis A in 1988 in Shanghai had an overall attack rate of 4083/100,000 population (292,301 cases). The epidemic curve showed three peaks in January and February. A case-control study of 1208 matched pairs supported that clams were the vehicle for the virus (summary odds ratio, 9.47; P less than .001). Analysis of subsets who had eaten clams indicated that only 3.5% with hepatitis A had cooked their clams compared with 18.1% without hepatitis A, and those with the disease consumed more clams. A historical cohort study indicated that approximately 31.7% of the population had eaten clams one or more times between 9 December 1987 and 3 January 1988. The estimated attack rates in those who had and had not eaten clams were 11.93% and 0.52%, respectively (relative risk, 22.94; attributable risk, 11.41%). The three peaks in the consumption curve correlated with those in the epidemic curve. Hepatitis A virus was demonstrated in clams taken from the Shanghai markets and from the catching area.

A DNA helicase from human cells.

We have initiated the characterization of the DNA helicases from HeLa cells, and we have observed at least 4 molecular species as judged by their different fractionation properties. One of these only, DNA helicase I, has been purified to homogeneity and characterized. Helicase activity was measured by assaying the unwinding of a radioactively labelled oligodeoxynucleotide (17 mer) annealed to M13 DNA. The apparent molecular weight of helicase I on SDS polyacrylamide gel electrophoresis is 65 kDa. Helicase I reaction requires a divalent cation for activity (Mg2+ greater than Mn2+ greater than Ca2+) and is dependent on hydrolysis of ATP or dATP. CTP, GTP, UTP, dCTP, dGTP, dTTP, ADP, AMP and non-hydrolyzable ATP analogues such as ATP gamma S are unable to sustain helicase activity. The helicase activity has an optimal pH range between pH8.0 to pH9.0, is stimulated by KCl or NaCl up to 200mM, is inhibited by potassium phosphate (100mM) and by EDTA (5mM), and is abolished by trypsin. The unwinding is also inhibited competitively by the coaddition of single stranded DNA. The purified fraction was free of DNA topoisomerase, DNA ligase and nuclease activities. The direction of unwinding reaction is 3' to 5' with respect to the strand of DNA on which the enzyme is bound. The enzyme also catalyses the ATP-dependent unwinding of a DNA:RNA hybrid consisting of a radioactively labelled single stranded oligodeoxynucleotide (18 mer) annealed on a longer RNA strand. The enzyme does not require a single stranded DNA tail on the displaced strand at the border of duplex regions; i.e. a replication fork-like structure is not required to perform DNA unwinding. The purification of the other helicases is in progress.